The choice between single chamber versus dual chamber pacing for sick sinus syndrome is critically dependent on the relative quality of life achieved by patients with each of these pacing modes, and on the relative cost-effectiveness. The proposed research will analyze health status and other dimensions of quality of life in patients randomized to dual chamber versus single chamber pacing, determine whether there are any differences in the relative benefits of either pacing modality in men versus women or in patients above age 75 years of age versus those less than 75 years of age, and assess the correlation of changes in health status and quality of life with changes in cardiovascular function and with the development of specified cardiovascular events. The research will also measure the comparative costs of the two pacing modes, in terms of both direct and indirect medical cost and non-medical costs, and compare their cost- effectiveness. The quality of life and cost-effectiveness research will be conducted as part of a Core Clinical Proposal which will randomize 2,000 patients in a trial of single chamber versus dual chamber pacing. In addition to the usual clinical outcomes that will be assessed as part of the core proposal, the quality of life and health status core laboratory of the current proposal will assess health status using the Medical Outcomes Study Short Form - 36, and two measures of utility in a subset of 1,400 randomly chosen patients at entry and annually for three years after enrollment. Cost will be determined by use of a detailed questionnaire that will be administered at these same time intervals. The incremental effects of pacing chamber mode on health status, quality of life, and cost-effectiveness determined after controlling for any baseline differences in patient characteristics, co-morbidities, or severity of illness using linear regression analysis. Any incremental differences in health status, quality of life, and cost-effectiveness between the two pacing modes will be compared with the incremental benefits and costs that can be achieved with other alternative allocations of health care resources. Based on the results, it will be expected that recommendations be made regarding preferences for pacing mode from the perspective of both the patient and society.